Foam Improved Oil Recovery: Effects of Flow Reversal

该项目的背景是提高石油采收率。在石油开采作业中，只有一小部分石油在储层自身压力下流出储层。之后，石油工程师们采取向储层中注入流体的办法，试图挤出剩余的石油。（由分散在含水表面活性剂液体中的气泡组成）是一种很有前途的候选注入流体，以实现这一目标。由于油气藏难以进入，（beingunderground地下and often经常in harsh苛刻environments环境），通常不可能直接观察注入的泡沫如何在它们内部流动。因此，建立储层流动的数学模型是非常有价值的。本项目将开发一个这样的模型，所谓的“压力驱动增长”，其在计算上特别有效，因为其仅关注泡沫前沿，因为其传播通过储层，而不是关注整个储层远离前沿的状态。尽管其计算效率高，压力-驱动增长模型目前有一些局限性。其中一个局限性是，该模型目前无法描述泡沫的情况，前缘的方向突然改变。这是一个问题，因为在泡沫提高采油过程中，如果一个新的相邻注入井上线，在泡沫注入给定井一段时间后已经在储层内的泡沫可能会改变其运动方向。本项目的目的是调整压力驱动增长模型来描述这种情况。然而，为了做到这一点，我们需要先探索另一种模式（即所谓的“分流”理论），它是压力驱动增长的基础。分流理论实际上比压力驱动增长包含更精细的细节，提供了关于在气体和液体相遇的泡沫前沿发生了什么的非常具体的信息。这些信息包括气体和液体分数分布如何在泡沫前沿变化，它的前部有多厚，以及它有多移动的：所有这些信息然后输入到控制由压力驱动增长给出的不太详细的描述的参数中。因此，我们的目标是探索分流理论如何响应流动方向的变化，并使用分流结果来重新参数化压力驱动增长。实现了这一点，我们的目标将是在许多涉及流动方向变化的石油工程情况下测试参数化的压力驱动增长模型。模型的结果也将与计算密集度高得多的"整个边界“方法进行比较，其通常用于石油工程。受益的主要应用领域当然是石油和天然气，石油和天然气工业设法回收更多的流体并因此从现有站点产生更多的收入。在某些情况下，例如对于非常成熟的油田，使用泡沫提高石油采收率甚至可能决定油田是保持开放还是需要关闭。通过使用建模工具预测泡沫提高石油采收率的进展，石油公司将能够在进行任何昂贵的钻探之前，从而限制了诉诸试错方法的必要性。尽管该项目的好处主要集中在石油和天然气上，但也预计会产生更广泛的好处。我们将研究的油藏泡沫前沿的前沿传播模型与管理许多其他系统的模型非常相似，包括固液悬浮力学、空气中的超音速流动、流行病传播、行人流动和火灾前沿传播等。因此，该项目可以为其他系统提供新的见解。

The context of this project is improved oil recovery.In petroleum extraction operations, only a fraction of the oil managesto flow out of a reservoir under the reservoir's own pressure.After that, petroleum engineers resort to injecting fluids into thereservoir to try to push out remaining oil.Foam (consisting of bubbles of gas dispersed in aqueous surfactantliquid) is a promising candidate injection fluid to achieve that.Because oil and gas reservoirs are difficult to access (beingunderground and often in harsh environments), it is generally notpossible to observe directly how an injected foam flows inside them.Having a mathematical model of the reservoir flow is thereforevery valuable.This project will develop one such model, so called ``pressure-drivengrowth'', which is particularly computationally efficient, as itfocusses just on a foam front as it propagates through the reservoir,rather than on the state of the entire reservoir away from the front.Despite its computational efficiency, the pressure-driven growth modelcurrently has a number of limitations.One such limitation is that the model is not currently able todescribe a situation in which the foam front undergoes a sudden changein direction.This is an issue since, during foam improved oil recovery, foam thatis already within the reservoir after a period of foam injection intoa given well, may change its direction of motion if a new adjacentinjection well is brought online.The purpose of this project is to adapt the pressure-driven growthmodel to describe situations such as this.However in order to do this, we need first to explore another model(namely so called ``fractional flow'' theory) which underpinspressure-driven growth.Fractional flow theory actually contains a finer level of detail thanpressure-driven growth does, providing very specific information aboutexactly what is happening at a foam front at which gas and liquidmeet.Such information includes how gas and liquid fraction profiles varyacross the foam front, how thick the front is, and how mobile it is:all this information then feeds into parameters governing the lessdetailed description given by pressure-driven growth.Our aim therefore is to explore how fractional flow theory responds tochanges in flow directions, and to use the fractional flow results tore-parameterise pressure-driven growth.Having achieved this, our objective will be to test there-parameterised pressure-driven growth model in a number of petroleumengineering situations that involve flow direction changes.Results from the model will also be compared against a much morecomputationally intensive ``entire reservoir'' approach, which isconventionally employed in petroleum engineering.The main application area that will benefit is of course oil and gas,with the oil and gas industry managing to recover more fluids andhence generate more revenue from existing sites.In certain cases, e.g. for very mature oil fields, employing foamimproved oil recovery might even make the difference between keeping afield open or needing to shut it down.By using modelling tools predicting how foam improved oil recoveryproceeds, oil companies will be able to plan and optimise operations,prior to performing any costly drilling, thereby limiting the need toresort to trial and error approaches.Although benefits of the project focus mostly on oil and gas, widerbenefits are also anticipated.The front propagation models that we will study for foam fronts in oilreservoirs are remarkably similar to models governing a number ofother systems, including mechanics of solid-liquid suspensions,supersonic flow through air, spread of epidemics, pedestrian flow andfire front propagation, amongst others.New insights into other systems such as these can therefore derivefrom the project.